Plugs of electrically insulating material are already known in the prior art. For example, patents already disclose electric connectors having particular shapes of position coding means to allow a selective positioning relative to a reception device. In a similar way, the prior art discloses the use of multiple coding keys which may be assembled and placed in various positions in order to realize several combinations of unique codes between the recesses of the connectors and the connecting elements. However, the above-mentioned documents mostly disclose coding keys designed to be typically used outside the openings of the box housing the connectors, which is provided for supporting electric contacts.
In particular, the DE-A-2,455,409 and U.S. Pat. No. A-4,478,469 appear to show the use of locking or coding elements conceived to be disposed in the same slots or openings of the connector box, which are used for receiving the electric contacts. However, neither of these two documents, nor any of the above-mentioned prior art, discloses the use of an insulating plug which, not only is insertable inside the same openings or recesses as those intended to receive the connecting electrical contacts, but also has two resilient areas, i.e., one having a connecting function in one opening of the connector box and the other to be inserted in an opening of the printed circuit board.